The present invention provides for two advantages. In previous types of double-flapper check valves, hinge and stop pins are installed through holes which extend through the wall of the valve body. After installation of the pins, the holes are sealed by plugs or other means. While initially effective, there is a possibility of leakage from the inside to the outside past the seals.
Another disadvantage of the previous designs is that the flappers are free to move sideways in the bore. This sideways movement causes extra wear on the wall of the flapper hinge or bushing, depending upon actual design.
One modification made to avoid holes through the wall is to mount pins in inserts which fit into cavities machined into the inner surface of the body wall. These inserts are retained in place by various means. U.S. Pat. No. 4,694,853 describes and illustrates the various embodiments in which hinge pins and stop pins are mounted in insert position in recesses in the body wall.
Although holes through the body wall are eliminated, and thus also potential leak paths, the modifications using inserts are expensive to manufacture and the design can restrict the particular type of gasket that can be used. Thinning of the wall occurs, which is not desirable. Also, the holes through the inserts for the hinge pins are round and permit sideways movement of the hinge pins which causes wear and increased maintenance of hinge parts and of the seal faces.
In the parent applications mentioned above, the flapper hinge pins have no clearance in the hinge holes in the flappers but have clearance only in the axial direction in the keepers or holding members. It has now been found that equivalent results can be obtained by having the clearance or elongated holes in the hinge on the flappers themselves.
The present invention provides for the flappers to be moveable at their hinge in the direction of the valve axis. The keepers or holding members for mounting the flappers, maintain the hinge pin on a fixed axis so that the pin does not travel axially.
By the present invention, replaceable flappers (or flappers plus seat ring) are provided in which the hinge holes in the flappers are elongated in the direction of the valve axis to allow movement of the flappers off the seat or toward the seat but not sideways. This movement has been found to minimize wear both on the hinge parts and on the seal faces.